mixing/mastering Q

[Royal de Capitator]

My question has to do with loudness...

Laptop output goes from 1/8th inch to RCA into a Vestax DJ mixer, then to my Mackie 624s.
I notice when I play songs or shows I didn't create that they are significantly louder than tracks I've made w/ FL Studio. (on the mixer I keep channel volume at max, master volume is in the middle, trim set to 0).  Most shows or tracks I listen to sound just right with these settings.

With stuff I've made, I need to turn the trim up about half way to get desired volume, even though I've got things pretty much as loud as they can be in FL Studio without going over 100% or too much clipping.
So far I don't use compression or limiting on my "masters" because it adds distortion beyond what I want.   It seems I'm missing something when it comes to getting it loud enough without sounding like crap.   Any help would be appreciated.

[just john]

One step I go through in my decidedly non-pro mastering process is
manually locating the most out-sticking peaks in the audio and
manually damping them a tad. On my old G4, the coincidentally-named
Peak is great for this, and Audacity does the trick on my other
machines.

I zoom the audio's display so I can see individual ... what do you
call one instance of a waveform? I mean, one trip from zero to one
direction, back thru zero, to the other direction, and back to zero.

(That's a bad description. Maybe a bad attempt at type-based graphics
will help.)

I zoom in until I can see /\/\/\_/\ level of detail. That's where
you can really see the peak as only a few bumps that need smooshing.

ANYWAY, I repeat the above until the post-normalization signal has the
average volume I want.

(You probably know this already. If so, forgive the kludgey way I
described it.)

[just john]

Oh, PS: I remember a similar problem I had some years back, that was
solved by removing DC offset.

[Royal de Capitator]

I'll give that a whirl, but it seems like a lot of work for a 6 minute song.  All this digital crap is 'spose to make life easy right?!  I've been playing with the tools in Audacity a little but it's really just playing.  I have no "pro" training at all, just knowledge I've gleaned from various forums like this. 
I think I remember from my fiddling that DC offset was the closest to the easy answer I was hoping for.  Need to do more fiddling and research...